1. Field of the Invention
The present invention relates generally to electrically conductive layers or surfaces on non-conducting substrates and, more particularly, to an electrically conductive surface or pattern integrally formed with a non-conductive ceramic substrate using lasers.
2. Brief Description of the Prior Art
The use of ceramics in the production of capacitors is widely known. In such capacitors, thin ceramic layers or ceramic coatings are bonded to metal substrates. Ceramics are used for their higher dielectric strength and durability against heat. Traditionally, alumina ceramic has been used in conjunction with metals such as copper and aluminum because of the ease of availability. However, prior art devices using these materials have significant shortcomings. There is poor bond development between the alumina ceramic and the various metal electrodes. Further, the combination of alumina ceramic materials with copper or aluminum electrodes has been found to be incompatible at elevated operating temperatures. There have also been recurring problems related to low dielectric properties and bond failure between coatings when used at high power levels.
U.S. Patent No. 5,391,841 to Quick teaches laser processing of ceramic coatings on electronic circuit substrates. A thin ceramic layer, such as alumina, is plasma spray deposited on a relatively thick metal substrate as a heat sink for improved dielectric and thermal properties which are produced by laser-reflow and recrystallization. This laser-reflow and recrystallization provide a different ceramic of higher dielectric and denser structure. Subsequent to the laser treatment of the plasma spray deposited ceramic layer, a metal coating is plasma spray coated onto the ceramic layer. Laser treatment of the ceramic layer apparently improves bond development between the substrate and the ceramic layer.
There is a general problem with adhesion of coatings on metal substrates and there is always the potential for delamination of a coating from the substrate to which it has been applied. This is particularly true if the coefficients of thermal expansion of the substrate and the coating applied thereto are not closely matched when the devices are to be used at elevated temperatures.